My 1997 chevy 1 ton truck hydroboost has developed a ...

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My 1997 chevy 1 ton truck with hydroboost has developed a soft brake pedal and I can not stop quickly why? It has a new hydrboost, master cylinder, calapers and pads all around. Worked fine untill a week ago the pedal went half way to the floof with very little stopping power. Then pushed my foot to its original position of about a 1" from max up position and stopped well. When I finished my task (about 1 hour) it gave me a soft pedal and is continuing that after all this expense.

hello, i dont think you have a hydro boost concern, normally the hydro boost only aids in making it easier to push pedal. if the hydro booster was at fault in most cases you would have a hard pedal. souns like there is air in the brake system. can i ask is there a reason why all these parts where replaced??? for this concern or a another problem??

There is no air in the system they were bled properly and fully.
The parts were changed because when the inspection for frozen/broken/worn parts, was done. The brakes pads were worn at about 70% so they were changed and I did not like changing these parrts with out changing all parts related. this truck ia a dually with disc brakes front and rear, with abs. When this soft pedal happened, the fluid level was checked and it was at full level. and does not diminish.

I do not recall, the diesel engine is noisey and I may not have noticed.
I had a suspicision that the problem is in the ABS unit I asked the technician and he said no way.
It feels like the fluid is being recirculated to the reservoir.

it would look at the anto lock brakes real closely. the chevy trcks are very well know for low speed abs activation. which is usually a wheel speed sensor sending a irractic reading, causing the abs to activate when it shouldnt. and if the problems only occurs at times may very well be a abs problem. here is a service bulletin on this matter please read and see what you think

Rotate the wheel with hand speed and measure the ACmV's. The reading should be at least 350 ACmV's.

If the reading is between 200 and 350 ACmV's, remove the wheel, caliper and rotor in order to gain access to the speed sensor.

Remove the wheel speed sensor and plug the hole to prevent debris from falling into the hub during service.

Clean the wheel speed sensor mounting surface using a wire brush, sand paper, emery cloth, ScotchBriteTM, or other suitable material. Be sure to thoroughly clean the wheel speed sensor surface. There should be no rust or corrosion.

Check the sensor head to determine if it has been warped/distorted due to the corrosion build up or other causes. Check the mounting surface on the sensor head for flatness by placing it on the edge of a metal machinists scale or other suitable straight edge to measure the flatness. Check the sensor for flatness in multiple (minimum 3) positions/directions. If the sensor head is distorted, replace the sensor.

When the corrosion inhibitor is dry to the touch (about 10 minutes), apply a thin layer of bearing grease to the hub surface and sensor O-ring prior to sensor installation. Use ONLY Wheel Bearing Lubricant, P/N 01051344 (Canadian P/N 993037).

Install either the original sensor or a new one in the hub and secure the sensor. Ensure that the sensor is seated flush against the hub.

Install the rotor, the caliper and the wheel.

Place the DVM across the sensor terminals and recheck the voltage while rotating the wheel by hand. The voltage should now read at least 350 ACmV's.

I have tried the brakes at different speeds from 50 mph to less than 5 mph and the brakes respond the same at any speed. That is why I did not suspect the sensors. Is the sensors active at any speed, or do the look at wheel speed to vehicle speed?
Is there any way the abs can be made inert to test if the problem is in the abs. There has been no abs light error displayed at any time.

Master Cylinder Diagnosis

Check for a cracked casting or brake fluid leaks around the master cylinder. A leak will have at least one drop of fluid. A damp condition is normal.

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Check the pedal linkage for binding and for incorrect pushrod length. If you do not find improper brake pedal travel or brake pedal binding disassemble the master cylinder. Refer to Master Cylinder Overhaul .

Hydraulic Booster Functional Test

The hydraulic booster uses fluid pressure from the power steering system. A malfunctioning power steering system can affect the hydraulic booster. A malfunctioning booster can affect the steering system. Before beginning extensive testing, perform the following procedure.

Check all power steering and brake pipe connections for leaks and restrictions.

review this information and runs some of the basic test to verify what is working like it is supposed too. then maybe pull abs fuse out and roadtest and see if problems reoccurs. anything you dont understand please ask me to explain

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